Influence of sulfide and temperature on species composition and community structure of hot spring microbial mats

In solfataric fields in southwestern Iceland, neutral and sulfide-rich hot springs are characterized by thick bacterial mats at 60 to 80 degrees C tha t are white or yellow from precipitated sulfur (sulfur mats), In low-sulfid e hot springs in the same area, grey or pink streamers are formed at 80 to 90 degrees C, and a Chloroflexus mat is formed at 65 to 70 degrees C. We ha ve studied the microbial diversity of one sulfur mat (high-sulfide) hot spr ing and one Chloroflexus mat (low-sulfide) hot spring by cloning and sequen cing of small-subunit rRNA genes obtained by PCR amplification from mat DNA . Using 98% sequence identity as a cutoff value, a total of 14 bacterial op erational taxonomic units (OTUs) and 5 archaeal OTUs were detected in the s ulfur mat; 18 bacterial OTUs were detected in the Chloroflexus mat. Althoug h representatives of novel divisions were found, the majority of the sequen ces were >95% related to currently known sequences. The molecular diversity analysis showed that Chloroflexus was the dominant mat organism in the low -sulfide spring (1 mg liter(-1)) below 70 degrees C, whereas Aquificales we re dominant in the high-sulfide spring (12 mg liter(-1)) at the same temper ature. Comparison of the present data to published data indicated that ther e is a relationship between mat type and composition of Aquificales on the one hand and temperature and sulfide concentration on the other hand.